Catalysts are widely used in process industries to facilitate many classes of important reactions including, but not limited to, chemicals manufacture, fats and oils manufacture, pollution abatement and petroleum processing. Use of catalysts for production of fuels and chemical feed stocks from petroleum will continue to grow due to (1) economic pressures to upgrade heavier crudes and other feeds with higher levels of impurities, (2) competitive pressures to achieve higher conversions using less energy, and (3)pressures to increase reaction selectivities to minimize waste production.
All catalysts gradually lose activity due to coking, poisoning by metals, sulfur, or halides, or loss of surface area due to sintering at high process temperatures. Regeneration is possible where the catalyst deactivation can easily be reversed. For example, naphtha reforming catalysts are routinely regenerated by removal of a carbon accumulation and reused for multiple cycles. However, the economic life of catalyst is ultimately limited by regeneration costs and the extent of irreversible deactivation.
As waste disposal regulations become more stringent and disposal of spent catalyst becomes more costly, clean alternatives for spent catalyst recovery or disposal become an increasing factor in waste minimization strategies. Presently, more than 50 million pounds of spent hydrocracking, hydrotreating, and naphtha reforming catalysts are consumed every year by the U.S. petroleum refining industry alone. Spent catalyst is typically disposed of in land fills or, if the metals value is high enough, sold to a metals reclaimer. Reclaiming spent catalyst materials typically involves conventional metallurgical processes, such as roasting, acid leaching, caustic dissolution, reactions with H.sub.2 S or Cl.sub.2, and calcination.
Petroleum hydroprocessing has been widely used by oil refiners for the past several decades to upgrade heavy crude oil fractions into marketable fuel products. Hydrotreating and hydrocracking processes are conventionally carried out in a fixed-bed, trickle-flow reactor. However, future advances in conventional fixed-bed catalysts and processes are expected to yield only marginal improvements.
Recently, petroleum research has included development of "slurry hydroprocessing" which may be the next generation of heavy oil upgrading processes. Much higher conversions are expected to be possible by using slurry catalysts than conventional pellet or shaped catalysts because of a higher surface area for contacting. Advantages of slurry processing include, a) higher conversion of residual crude (via cracking) to more valuable transportation fuels, b) better removal of sulfur and nitrogen from the fuel, and c) better removal of metals (i.e., Ni, V) that poison catalysts in other refinery units. Refinery profits have been, and will continue to be, increasingly dependent upon the refiner's capability to upgrade residual oil, otherwise typically referred to as the "bottom of the barrel". Slurry hydroprocessing shows enormous potential for increased profits in utilizing such residual oil.
Although slurry hydroprocessing is a promising approach for heavy oil upgrading, such has not seen commercialization as of this date. Part of the problem is believed to be centered on the catalyst material. Candidate catalysts, such as Mo, Ni, Co, and W, can provide good activity and stability. Since these catalysts are fairly expensive, they would have to be recovered and recycled for any slurry hydroprocessing process to be economical.
However, it is costly to recover many types of spent catalysts in an environmentally acceptable manner. For example, spent catalysts from petroleum residuum hydrotreating are typically encased in "coke balls". Such principally comprise very high-boiling carbonaceous material, and also include metal sulfides of Ni and V which are considered contaminates. Presently proposed techniques for recovering such catalysts include coking, roasting and acid or base leaching. These operations typically operate under severe acid or base conditions and/or generate polluting byproducts. Hazardous or toxic chemicals are used in conventional processes. In addition, the energy requirements of operating equipment such as roasters would be substantial.
Needs remain for methods of recovering catalyst material from reaction waste material solids and other latent catalyst material solids for the petroleum and other industries.
The subject mater of the present invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of operation, together with further advantages, may best be understood by reference to the following description taken in connection with the accompanying drawings wherein like reference numerals refer to like elements.